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Discussion Starter #1
I've been noticing a drop in volts when I turn on the AC or cooling fans kick in (usually goes from the normal 14 volts on the gauge to around 13 (I measured about 13.6 volts on the voltmeter). Volts measure 14.3-14.4 on the voltmeter when I first start the car, maybe 13.8-13.9 when hot idle and no load on alternator.

I also notice the volts briefly when I apply the brakes but they come back to normal again.

Is this a normal thing or am I about to have another bad alternator? I just got back from a decent 30 minute ride, checked the battery with the voltmeter after shutting the car off and it was 12.8 volts (which to me seems like the alternator is properly charging the battery). Just weird that the volts drop at times, especially if they stay lower with the cooling fans and/or AC.

Thanks!
 

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Voltage drop when using high draw items like cooling fans & brake lights is common. Since ac puts quite a big load on engine, voltage can drop also. This could be a sign of belt slippage. But unless voltage drops below 13, I wouldn't worry too much.

Just make sure belt is good and tensioner bearing assembly is good.
 

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Discussion Starter #3
Belt and tensioner replaced last year. Also tried a different alternator (I have a spare), same thing.

Anything else I should be checking? Thanks!!
 

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You still might check belt tensionier. Even though it's fairly new, it could still be bad. Check the travel of the tensioner. If it has to go to the very end of it's travel, belt tension might be allowing belt to slip on alt.

But, I wouldn't worry unless voltage drops way down.
 

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Discussion Starter #5
Thing is, it started happening recently out of the blue. What really worries me is it happens anytime a load is put on the electrical system (even when the air pump kicks in after a cold start). I know the volts are dropping because when they drop, so does my interior lights.

No idea, nothing changed except I had valve lifters replaced in May. I checked one of the grounds on the passenger side motor mount, seemed fine (wondering if there are other grounds I need to look at). If that checks out I might need to take it to the shop and have them look at it.
 

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If you've downloaded the 96 service manual, it will have all the grounds that car has. In the wiring diagrams. As GM changed the format of it's service manuals in 96, things are somewhat harder to find then in the 93-95 manuals.

But keep looking and you'll find the ground wiring. You might even want to download the 94 or 95 manual. Grounds are something that should have remained pretty consistent. in the 4th gen cars. 94 & 95 manuals are much easier to find wiring diagrams

Ground diagrams start on page 8A-14-1. Component location diagrams will show most all the grounds. They start on page 8A-201-0
 

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Discussion Starter #7
One more thing I noticed when I turn the key (ignition on but not starting engine)....

The volts do not climb smoothly on the gauge anymore. Instead, the volts jump briefly above the actual voltage before the needle goes to the actual voltage.

Taking it to the shop today.....wish I knew what was wrong (hope they will be able to figure out what's wrong). Hoping it's not the computer or BCM, or gauge cluster (I have a digital odometer so if they replace the cluster would that mess up the miles)?
 

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I believe the miles are stored in pcm.

I noticed that is earlier posts you had different readings from gauge and test equipment. You could have a problem with the volt meter in instrument cluster. Or in the wire that voltage info is sent to instrument cluster. Or even a bad ground to gauge.

All the instruments rely on the plastic printed circuit on back of cluster. Torn areas on printed circuit, or even corroded contacts of gauges can make a difference.
 

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Discussion Starter #9
Do the gauges have some kind of "filter"? Strange how the volts immediately jump abruptly when I turn the key to ignition before starting, rather than the volts smoothly rise to the actual volts like it used to.
 

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93 cars had a tach filter but v oil pressure, coolant temp & gas gauges run strictly off resistance of senders. Pluss they get power, & ground.

Volt gauge is simpler. It gets its volt info from a power wire and has a ground.

Since I'm not as familiar with the obd 2 cars of 96 & 97, you'll have to look up in 96 manual and see if BCM has any control of gauges.
 

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Discussion Starter #11
Ok it's at the shop, they did an electrical inspection which seemed to pass, nothing is shorting out. They think the stepping motor is going out on the volts gauge (now I'm thinking it's also going out on the oil gauge since that is also fluctuating). If that's the case I should probably have them do all the gauges...
 
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